\begin{tikzpicture}
    \pgfmathsetmacro{\R}{1.5}

    \tkzDefPoints{0/0/O}
    \tkzDefPoint(210:\R){A}
    \tkzDefPoint(330:\R){B}
    \tkzDefPoint(270:\R){C}
    \tkzInterLL(A,B)(O,C)  \tkzGetPoint{D}

    \tkzDrawCircle[very thick](O,A)
    \tkzDrawArc[very thick, pattern={mylines[angle=55, distance={4pt}]}](O,A)(B)
    \tkzDrawSegments[very thick](A,B  O,C)
    \tkzDrawSegments[dashed](O,A  O,B)
    \tkzMarkRightAngle[size=.2](B,D,O)

    \tkzLabelPoints[above](O)
    \tkzLabelPoints[left](A)
    \tkzLabelPoints[above right](B)
    \tkzLabelPoints[below](C)
    \tkzLabelPoints[above left](D)

    \tkzDefPointOnLine[pos=1.5](D,B)  \tkzGetPoint{b}
    \tkzDefPointBy[translation=from D to b](C)  \tkzGetPoint{c}
    \tkzDefShiftPoint[b](0,.5){b'}
    \tkzDefShiftPoint[c](0,-.5){c'}

    \tkzLabelSegment[above, rotate=30](O,A){\small 12cm}

    \tkzDrawLines[add=0 and 0.1](D,b  C,c)
    \tkzDrawSegments[-Latex](b',b  c',c)
    \tkzLabelSegment[centered, rotate=90](c,b){\small 6cm}
\end{tikzpicture}

